Despite the fact that sex is an activity generally done lying down, a new study out of the University of Quebec in Montreal found that it's actually a respectable calorie burner. As a rare hybrid of gym rat and lazy sloth, I am all for trying to combine a workout with things I do in my warm, comfy bed. Jessica Matthews, exercise physiologist for the American Council on Exercise, confirmed it's possible. "Sex can burn 3 to 4.5 calories a minute and more, depending on how vigorous it is," she told me. Oh, it would be vigorous. Armed with goodies like the Forerunner 220 (the latest fitness watch from those geniuses at Garmin) and my "workout partner," aka my husband, Greg, I decided to go for the burn.

The lowdown

First up, arms. I cranked out three sets of 10 push-ups while on oral duty, pausing between sets to give my guns a rest and to work my abs by holding a plank. My arms were trembling, and a thin film of sweat covered my pits and upper lip. I know what you want to ask, and the answer is yes, it is hard being this sexy.

Squat thrusts

Next, leg work. I positioned a yoga mat near the kitchen counter. Greg lay on it, and I crouched over his lap, feet on either side of his hips, turning my back to him. I pressed the timer on my watch and held on to the counter while I did mini-squats for 60 seconds. Recovered. Eyed some cookies and almost quit but persevered with two more sets.

Tummy tamer

We moved to the bedroom for the abs portion of the workout. Greg stood at the foot of the bed while I stuck my legs straight up in the air, holding a medicine ball above my head. While Greg thrust, I crunched, bicycled and scissored my ankles until my abs weren't the only thing screaming in response. (Wink, wink.)

To the finish

Sprint time! I synced my watch to a heart-rate monitor and went for the O. I started out at 59 beats per minute, and the first orgasm brought that to 127—it takes running on a treadmill at a 7.7 on a 3 percent incline for a minute to get my heart rate that high. It dropped down to the 80s, then climbed up to 117 again with O number two. I was aiming for three "sprints," but I am only human, and, well, so is Greg. The whole experiment took 40 minutes, which means I burned roughly 180 calories—a hefty glass of wine. My arms and lower abs were sore later, proof I got my fitness on. I wouldn't give up Physique 57, but it's not a terrible option for when I'm all out of clean sports bras and too lazy to do laundry.